This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Expression of tight junction proteins between brain microvascular endothelial cells (MBEC) of the blood-brain barrier (BBB) is lost during development of HIV encephalitis (HIVE). While many studies have focused on the strains of virus that induce neurological sequelae or on the macrophages/microglia that are associated with the development of encephalitis, the molecular signaling pathways within the BMECs involved have yet to be resolved. We have previously shown that there is activation and disruption of an in vitro BBB model using lentivirus-infected CEMx174 cells. We and others have shown similar disruption in vivo. Therefore, it was of interest to determine of the presence of infected primary macrophages could disrupt intact cerebral microvessels immediately ex vivo, and if so, which signaling pathways were involved. Our data demonstrate that disruption of tight junctions between BMECs is mediated through activation of focal adhesion kinase (FAK) by phosphorylation at TYR-397. We also show that myosin light chain kinase (MLCK) is also phosphorylated in the same time course as FAK. Inhibition of FAK activation is sifficient to prevent tight junction disruption. This, it may be possible to inhibit the development of HIVE by using inhibitors of FAK and MLCK.